This invention relates generally to laser beam projectors, and more particularly to a method and device for controlling and delivering power to a laser and communicating information from said laser to a remotely positioned sensor assembly. The invention has particular application for making measurements as well as machine control, such as with earth moving and construction equipment
A common use of laser beam projectors in the construction industry is for ensuring that a trench or surface is of the proper and constant depth. The laser beam projector is placed at a fixed, known height, and an array of sensors senses the impingement of the laser beam. Depending on which sensors are impinged, the height of the receiver equipment relative to the laser beam projector can be determined.
While laser beam projectors come in a variety of different forms, this invention relates primarily to laser beam projectors which are capable of rotating. When the projector is in a rotation mode, the sensors in the sensor assembly do not continuously detect the laser beam, but rather only detect the laser beam for a brief instant when the rotating laser beam sweeps past the sensors. Rotating the laser beam, instead of keeping it constantly pointed in one direction, enables the sensors to move laterally with respect to the projector without the need for realignment of the laser beam projector with respect to the sensors. Because the rotating laser beam only impinges the sensors for a brief instant, the power of the signal detected by the sensors is much less than if the beam were not rotating, but instead continuously pointed at the sensors. The reduction in power of the detected signals makes it more difficult for the sensors to detect the signal and to filter the signal out from other radiation sources detected by the sensors, such as ambient sunlight. The distance from the projector which the sensor can effectively operate is therefore reduced when the laser beam is rotated.
In certain applications, the distance between the laser beam projector and the sensor may be quite large, which may lead to additional difficulties besides the relative weakness of the signal detected by the sensor. One difficulty relates to the requirement of keeping the laser beam level. If the laser beam is not level, the sensor will yield a height measurement that has an error component which increases with increasing distance from the laser. The height error may not be acceptable for various applications. One mechanism for eliminating the condition of a non-level laser beam projector is to mount the laser on a gimbal which allows the laser to generally swing freely so that the laser beam assumes a true vertical orientation. Providing power to the gimbaled laser, however, often hinders its free movement. In the past, to overcome the hindrance of the power feed mechanism to the free movement of the laser has typically required complex and expensive designs of the power feed mechanism.
Large distances between the laser beam projector and the sensor assembly may also make it difficult for people working near the sensor to know the status of the laser beam projector. For example, if the projector is bumped or otherwise knocked from its level position, this fact may not be readily apparent to people in the vicinity of the sensor if the projector is far away. An off level projector leads to the problems discussed above. Other conditions of the projector may also be important to know for those working away from the projector.
In light of the foregoing, a need can be seen for a laser which overcomes the difficulties associated with a laser beam projector stationed a large distance from the sensor unit.